The stereoselective synthesis of spirocyclic pyrazo-
lin-5-ones by N-heterocyclic carbene (NHC) organocatalysis has
been less studied so far. For this reason and considering the interest
of this class of compounds, here, we present the NHC-catalyzed [3
+ 2]-asymmetric annulation of β-bromoenals and 1H-pyrazol-4,5-
diones that achieves to produce chiral spiropyrazolone-butenolides.
The synthesis is general for aryl and heteroaryl β-bromo-α,β-
unsaturated aldehydes and 1,3-disubstituted pyrazolones. The
spirobutenolides have been obtained in good yields (up to 88%)
and enantioselectivities (up to 97:3 er). This constitutes the first
described example using pyrazoldiones as the starting materials for
this class of spiro compounds.
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